Power modules are used in many application fields for various tasks, for example, to control the speed and power of electric motors. A circuit arrangement acting as power unit forms part of such power modules and typically has both active semiconductor components, such as power semiconductor components, and passive components, such as resistors (e.g., shunts for current measurement) and possibly capacitors. The power semiconductor components work in switched mode, which causes high rates of current change. These high rates of current change necessitate a low-inductance structure of the circuit arrangement to prevent overvoltages.
Consequently, and for reasons of adequate heat removal of their power dissipation, the carrier element used for the circuit arrangement""s active semiconductor components (particularly the power semiconductor components) is typically a so-called DCB (direct copper bonding) substrate, which is made of a ceramic layer enclosed by two copper layers (e.g., made of aluminum oxide Al2O3). The active semiconductor components (power semiconductor components) are soldered to the upper copper layer of the DCB substrate and contacted by means of bond wires. The upper copper layer of the DCB substrate is structured (interrupted) to form track conductors for connecting the power semiconductor components.
For mechanical stabilization and heat removal, the DCB substrate is mounted on a metal plate serving as circuit substrate, typically soldered. This metal plate transfers the heat loss to a cooling system.
The circuit arrangement""s passive components (particularly the resistors) are advantageously realized in thick film technology (i.e., printed on a ceramic substrate). This ceramic substrate, in a separate manufacturing step, is bonded to the circuit substrate adjacent to the DCB substrate (e.g., by means of heat conductive bonding).
The inherent disadvantage is that
separate process steps and technologies are required for soldering the DCB substrate and bonding the ceramic substrate to the circuit substrate, which is time-consuming and costly;
Connection (contacting) between the circuit arrangement""s passive components mounted on the ceramic substrates and the active semiconductor components mounted on the DCB substrates is problematic due to the spatial separation. This requires long connecting leads and connecting lugs, which as parasitic inductances have a negative effect on the properties of the circuit arrangement or power module (generation of overvoltages, EMV problems).
DE 35 38 933 A1 furthermore shows a power module in which the ceramic substrate carrying the passive components is soldered directly to the DCB substrate carrying the active semiconductor components. Here, the solder connection performs a pure fixation and heat conducting function. Although this eliminates the additional process step of bonding, a large number of bond wires continue to be required for electric contacting of the passive components with the track conductor structure arranged on the DCB substrate. Bond wires, however are costly and susceptible to mechanical stresses.
The object of the invention is to define a power module in accordance with the preamble of claim 1 with a simple structure and manufacturing process, in which these disadvantages are obviated.
According to the invention, this object is attained by the features of claim 1.
Advantageous further developments of the power module and a process for its manufacture are the subject of the additional claims.
In the inventive power module, at least a portion of the passive components is realized by means of thick film technology (e.g., by depositing on a ceramic substrate a first print layer as the actual component and at least one additional print layer laterally adjacent to the first print layer acting as contact surface). The ceramic substrate thus printed (the thick film circuit) is placed on the upper side of the DCB substrate (the upper copper layer) suitably structured to form track conductors and connecting surfaces and is connected with the DCB substrate by soldering the contact surface(s) to the corresponding connecting surfaces of the DCB substrate. Connection (contacting) with the other semiconductor components arranged on the DCB substrate can be suitably effected either directly via track conductors or via bond wires. The DCB substrate is suitably connected with the circuit substrate of the circuit arrangement, e.g., soldered to this circuit substrate (e.g., a metal plate). Power dissipation of the passive components (particularly resistors) arranged on the ceramic substrate is removed via the ceramic substrate and the DCB substrate to the circuit substrate. During production, the ceramic substrates with the passive components (the resistors) can be soldered to the circuit substrate simultaneously to soldering the active semiconductor components and/or simultaneously to soldering the DCB substrate to the circuit substrate so that no separate process step is required. In other words, soldering the thick film circuit (passive components on ceramic substrate) can be executed simultaneously with soldering the active semiconductor components to the DCB substrate or simultaneously with soldering the active semiconductor components to the DCB substrate and the DCB substrate to the circuit substrate.
In addition to the components realized in thick film technology, other components (e.g., SMD components) can be mounted on the ceramic substrate and connected with the rest of the circuit arrangement by means of contact surfaces.
The advantages of said for manufacturing a power module are that
production complexity and thus cost of the power module are reduced by the simultaneously performed soldering process required for the passive components (the resistors) onto the active semiconductor components;
a simpler and more compact structure results due to the low number of connecting leads of the circuit arrangement and the reduced lead length of the possibly still present connecting leads;
overvoltages, and thus impairment of the functioning of the power module, are prevented due to the shorter lengths of the connecting leads and the reduced parasitic inductances.